1. Field of the Invention
This invention relates generally to signal transmitter locating systems and, more specifically, to a Method for Real-time, Automatic, Wideband, High Accuracy 3D RF Direction Finding.
2. Description of Related Art
This patent application describes an enhanced method for locating radio frequency signal emitters.
Today's high frequency direction finding systems perform well in situations that require analysis on very few frequencies and when target signals are of constant frequency and long duration. However, these systems suffer from serious performance and cost issues in the face of short duration signals or situations that require analysis of the entire RF band. A modern RF DF system should process entire receiver bandwidths at speeds that enable it to analyze modern, short duration signals without introducing enormous hardware requirements and costs.
Current Direction Finding systems are narrow-band in nature, possessing bandwidths of a few Kilohertz (KHz) and requiring many RF receiver channels and DSP processors to digitize and process each narrowband channel. The results are then later stitched together. This approach is very costly for the subset of real-world applications, often referred to as wideband applications, which require the analysis of large segments of the Electromagnetic Spectrum. Generally, to keep costs down, fewer receiver channels are used which adversely effects processing efficiency as the system can only process small amounts of bandwidth simultaneously. In addition, further serial processing is required if elevation and azimuth are desired compounding both cost and efficiency problems.
What is needed therefore, in order to feasibly determine the angle of arrival (AoA) of RF emitters as efficiently as possible is a method that not only (1) operates on wideband data provided by a single receiver channel doing work that would normally require thousands of separate receivers, but also (2) calculates both azimuth and elevation results at numerous frequencies in parallel. Multipath results in errors in the determination of the arrival angles. By increasing the size of the antenna array so its diameter is larger than the wavelength substantial reduction of the multipath errors can be achieved. When the array diameter is larger than half the wavelength then special methods have to be applied in order to remove the ambiguities in the received relative phases. This patent application describes such a method.